a. Field of the Invention
The invention relates to methods for augmenting soft tissue using a needle-free jet injector, and to the needle-free injectors useful for such methods. The present invention is particularly useful for augmenting skin using a needle-free jet injector to fill lines, folds, and wrinkles in skin with dermal fillers such as collagen, hyaluronic acid, or a variety of biodegradable and nonbiodegradable polymers.
b. Background Art
As skin ages and is repeatedly exposed to the sun's ultra violet rays, dermal cells decrease their production of hyaluronic acid and increase the rate of its degradation. Likewise, aging skin loses collagen, another natural substance necessary to keep skin youthful and resilient. As shown in FIG. 1A, over time, the loss of hyaluronic acid and collagen causes aging skin to develop lines, wrinkles, and folds.
For the past few decades, patients have had a variety of options for augmenting soft tissue to fill undesired lines, wrinkles, folds, and scars. Originally, collagen was used for such soft tissue augmentation. More recently, hyaluronic acid in a variety of formulations has gained in popularity. Additionally, a variety of biodegradable and nondegradable products have been introduced or are in the process of regulatory approval for use as dermal fillers.
As shown in FIG. 1B, these soft tissue augmentation products are typically injected with a needle just below the surface of the skin, at the site of the wrinkle, line, or fold (or scar or dermal tissue to be enhanced). The products essentially plump up the skin from beneath the upper layers of skin. Some soft tissue augmentation products are instead implanted beneath the skin with an incision. In either case, the skin is cut or punctured with a needle or scalpel type instrument to insert soft tissue augmentation products into the desired location.
Use of needles and similar instruments puts health workers and patients at risk of infection through inadvertent needle-sticks or other equipment misuse. Additionally, needles and syringes are difficult to sterilize, and the use of improperly sterilized syringes and needles greatly increases the risk of blood-borne disease transmission among patients. While disposable syringes are typically used to alleviate the risk of disease transmission, these disposable units create hazardous medical waste and waste disposal problems. It is thus desirable to have a system for administering soft tissue augmentation products without the use of needles or similar devices.
In the 1930s, the first needle-free injectors were invented and patented. In the late 1940's, Hingson and Hughes reported a series of clinical, anatomical, and histological studies on jet injection of several drugs, in particular insulin, using a device called Hypospray. Interest in needle-free injection was substantially increased and jet injectors were used with several other drugs including penicillin, streptomycin, sulfones and vaccines against typhoid, diphtheria and tetanus, polio, and small pox.
Single-dose jet injectors, known as DCJIs (Disposable Cartridge Jet Injectors), are currently available and have been used for delivering insulin, growth hormones, vaccines as well as a variety of liquid drugs. Some DCJIs are only partly disposable (a disposable liquid reservoir in conjunction with a non-disposable actuation mechanism) while others are fully disposable.
Multidose jet-injectors were first described in the 1950s. Introduction of multi-use-nozzle jet injectors opened the door to mass immunization. The Press-O-Jet and Ped-O-Jet injectors were used for mass immunization against numerous diseases including poliomyelitis, influenza, typhoid, cholera, yellow fever, and smallpox all around the world.
Such jet injectors are typically used for intramuscular injection of typically freely-flowing liquid drugs. It is desirable to adapt a liquid jet injector for fairly accurate subdermal injection of viscous materials for soft tissue augmentation.